Modified kaolins

ABSTRACT

A process for the preparation of a modified kaolin from a kaolin group mineral which includes expansion and contraction of layers of the kaolin group mineral. The layers comprising one Si-tetrahedral sheet and one Al-octahedral sheet. The expansion and contraction may be initiated by initial intercalation of a reagent which can penetrate kaolin layers to reach an interlayer region therebetween to form an intercalate. Subsequently, the intercalation nay be followed by de-intercalation which involves the removal of the reagent. By the above process, there is provided crystalline modified kaolins having the following properties: (i) an increased interlayer space compared to corresponding kaolin group minerals; (ii) an increased susceptibility to intercalation by cations, anions or salts compared to corresponding kaolin group minerals; and (iii) an increased exfoliated morphology compared to corresponding kaolin group minerals.

FIELD OF THE INVENTION

Kaolin clays, composed of one sheet of tetrahedrally co-ordinated Si andone sheet of octahedrally co-ordinated Al, have a restricted capacity tointercalate as opposed to 2:1 structures of montmorillonites. Thislimited capacity to accommodate compounds from solution has meant littleuse of these abundant minerals as catalyst, sorbents or as porousmaterials, while montmorillonites have seen a continuous growth. Thecapacity of kaolins to intercalate can be enhanced by repeated expansionand contraction of layers, a process which modifies the atomic scalestructure of these minerals. The newly derived capacity of these claysmakes them useful precursors for preparation of adsorbents, catalysts,and porous materials.

BACKGROUND OF INVENTION

Clay minerals, also known as hydrous layer silicates, are part of alarger family of minerals called phyllosilicates or layer silicates. Aunit layer of a given clay mineral is typically composed of a twodimensional arrangement of tetrahedral and octahedral sheets, each withspecific elemental composition. The tetrahedral sheet may havecomposition of T₂ O₅ where T, the tetrahedral cation, is Si, Al and/orFe, and the octahedral sheet commonly contains cations such as Al, Feand Mg. A tetrahedral sheet containing only Si⁴⁺ cations is electricallyneutral, as are Mg-octahedral sheets and Al octahedral sheets with onethird vacant sites. Both tetrahedral and octahedral sheets can havecationic substitutions resulting in a net negative charge which isbalanced by interlayer cations. The type of sheets in a unit layer,degree of substitutions, and stacking of layers vary greatly, anddetermine the type and economic usefulness of a given clay mineral.

Clay minerals can be broadly classified into 2:1 and 1:1 type on thebasis of type of sheets in a unit layer. The 2:1 type clay minerals arecomposed of one octahedral sheet sandwiched between two tetrahedralsheets (FIG. 1). The upper tetrahedral sheet is inverted so that apicaloxygens point down and are shared by the octahedral sheet. When all thesites in the tetrahedral sheet are occupied by Si and all sites in theoctahedral sheet are occupied by Mg or two-thirds of the sites areoccupied by Al, the resulting layers are electrically neutral. Innature, these conditions are exemplified by talc and pyrophyllite,respectively. Electrically neutral layers of these minerals are coupledby weak dipolar and van der Waals forces. There is no driving force forattraction of interlayer cations or intercalating compounds. Therefore,these minerals have little use as exchangers or adsorbents.

In contrast to talc and pyrophyllite, layers in mica bear a net negativecharge of 1e per Si₈ O₂₀ unit due to excessive cationic substitutions inthe tetrahedral sheet. The resultant net negative charge is balanced byinterlayer K⁺, which is coordinated to the hexagonal array of oxygenatoms on either side of the interlayer space. The interlayer K stronglybinds the layers and resist intercalation and exchange processes forthese minerals.

While pyrophyllite-talc group and mica group minerals represent theextreme cases with either no or excessive charge, the smectite grouprepresent 2:1 clay minerals with an intermediate level of charge,usually ranging from 0.2 to 0.6 e per Si₈ O₂₀. Whilst the net negativecharge on smectites is sufficient to hold exchangeable cations and aprovide driving force for intercalation, it is not too excessive andlocalised, as in micas, to resist swelling of layers. The interlayercharge in smectites is usually balanced by intercalated alkaline earthor alkali metals which can be readily exchanged with desired cations.

Some smectites (such as beidellite and nontronite) derive their chargefrom substitutions in tetrahedral sheets, while others derive theircharge from substitutions in octahedral sheets. The layer charge intetrahedrally charged smectites is relatively localised, which resultsin greater three dimensional order and -poorer intercalation, swellingand exchange properties. In the octahedrally charged smectites, thelayer charge is uniformly distributed in the oxygen framework due to theoctahedral sheet being sandwiched between tetrahedral sheets. As aresult, the adjoining layers are randomly stacked with little threedimensional order. These octahedrally charged smectites, calledmontmorillonites, have been extensively exploited as sorbents,exchangers and pillared clays.

The 1:1 type clay minerals, the other most abundant clay mineral type,are composed of one Si-tetrahedral sheet and one Al-octahedral sheet(FIG. 2). Unlike 2:1 type minerals, the constituent sheets of all 1:1type clays have practically no cationic substitutions. As a result, 1:1layers are electrically neutral and lack cation exchange and swellingproperties which are the centre piece of montmorillonites.

While kaolins do not possess any interlayer net negative charge, their1:1 structure does have the advantage of having a polar interlayerregion due to 1:1 sheet configuration (FIG. 2). In other words, one sideof the interlayer space is lined with oxygens, while the other side islined by hydroxyls. This polar nature of the interlayer region canpotentially attract a variety of organic and inorganic compounds intothe interlayer. For these reasons, kaolins possess a limitedintercalation capacity while their electrically neutral 2:1 analogues,talc and pyrophyllite, exhibit no intercalation behaviour.

However, intercalation capacity of kaolins is restricted due to thelayers being strongly coupled by H-bonds between the surface hydroxylsof the octahedral sheet and basal oxygens of the tetrahedral sheet. Thestrength of interlayer bonding and consequent intercalation capacityvaries among various kaolins depending on the history of theirformation. Due to the interlayer region being protected from thereacting species by strong interlayer H-bonding, any exchange andreactivity in these minerals is generally provided by OH groups on theedges of the crystals, which only make a small proportion of total OHgroups present in the 1:1 minerals.

Besides this restrictive role, interlayer bonding also restricts theentry of intercalating molecules which are attracted to the polar natureof the interlayer region. Only some polar compounds such as potassiumacetate (KAc) and dimethyl sulphoxide (DMSO) are able to intercalatekaolins as opposed to a wide variety that can intercalate smectites.

In the scientific press, there is abundant literature on theintercalation capacity of kaolins particularly kaolinite and halloysite.Reviews by Wada, 1959, American Mineralogist 44 153-165 and Carr et al.,1978, Clays and Clay Minerals 26 144-152 list the compounds that canintercalate kaolin clays to some degree. As is evident in these reviews,kaolins can intercalate only some highly polar molecules or salts ofunivalent alkali metals such as potassium acetate and alkali metalhalides. Kaolins are, as these authors have stated in their reviews,unable to intercalate salts of divalent cations such as Ca, Mg, Cu, Nietc. This is the principal reason why kaolins have not been able to findextensive applications as sorbents, catalysts and porous materials.Clearly, successful intercalation or exchange of ions or molecules ofcertain divalent or trivalent metals into the interlayer is necessaryfor preparation of useful catalytic, adsorbent or porous materials fromkaolins.

Therefore, it is highly desirable to improve the intercalation capacityof the kaolin interlayer region so that desired organic or inorganiccompound may be intercalated into these clays. The new intercalationcomplexes thus formed can be then further treated using prior art ornovel processes to form new materials for applications in catalysis,ceramics, uptake of pollutants etc.

We have discovered that the ability of kaolin clays to intercalatecompounds can be increased many fold. The kaolin clays modified in thisway are able to readily intercalate compounds that make no or only weakcomplexes with untreated kaolins.

The 1:1 group clay minerals comprise the polymorphs kaolinite, nacrite,dickite and halloysite. Kaolinite, dickite and nacrite have a chemicalcomposition Al₂ Si₂ O₅ (OH)₄ and differ only in the manner in which the1:1 layers are stacked. Halloysite has the composition Al₂ Si₂ O₅(OH)₄.₂ H₂ O and differs from the other three polytypes in thatmolecular water occupies the interlayer site in its hydrated form.Kaolinite is most abundant in the kaolin group and has many applicationsin the paper industry, ceramics, electrical insulation and the like.This disclosure primarily describes results for kaolinite andhalloysite. However, it will be appreciated by those skilled in the artthat the invention applies equally to other members of the kaolin groupclays.

Kaolins occur widely in many parts of the world and are, in general,more abundant than montmorillonite clays. In tropical and subtropicalregions, kaolin clays are particularly common, and often overlieprecious metal ores deposits. Kaolin clays also commonly underliebauxite deposits such as bauxite deposits in Weipa, North Queensland,Australia. In such situations, kaolin clays are a cheap byproduct ofmetal or other ore mineral mining. Not all types of kaolins are suitablefor paper coating, ceramics and other current applications of kaolins.Consequently, much of the kaolin produced as a byproduct of miningactivity remains unused and poses a significant disposal problem.

Recently, there has been a renewed interest in utilising kaolin, andseveral new materials and processes have been disclosed which utilisekaolin clays as their raw material. For example, InternationalPublication No. WO96/18577 discloses a process to synthesise materialsof high cation exchange and moderate surface area by reacting kaolinclays with alkali metal hydroxides. A similar patent applicationInternational Publication No. WO95/00441 describes a process of treatingkaolin clays with alkali metal carbonates and hydroxides at elevatedtemperatures to produce material of high cation exchange but low surfacearea. In this set of processes the kaolin structure is completelydestroyed in highly basic or high temperature conditions and an X-rayamorphous material or a material of a structure completely differentfrom layered structure of kaolin is formed.

U.S. patent (U.S. Pat. No. 5,416,051) describes a process to preparepillared clays using kaolin clays. According to this disclosure,metakaolin is first prepared by firing untreated kaolin at temperaturessufficient to dehydroxylate kaolin and then treating the metakaolin withpillaring agents. The metakaolin prepared by calcining kaolin is aamorphous material structurally and chemically different from kaolin.

None of the disclosures in the patent literature or publications in thescientific literature attempts to enhance the intercalation capacity ofkaolin clays without radically destroying its structure.

Kaolins may find additional applications if new kaolin based materialscould be readily manufactured with desirable properties such as higherBET surface area and/or higher cation exchange capacity and/or higherdensity of active sites for applications such as catalysis.Additionally, the usefulness of these new materials made from kaolinswould be greater if only one of these properties were evident or ifother properties such as adsorption or uptake of other elements orcompounds were enhanced over that of unprocessed kaolinite. Theseelements and compounds may be in the liquid or gaseous state.

Accordingly, it is an object of the present invention to providemodified forms of kaolinite which show enhanced properties over that ofthe original starting kaolinite through treatment with a suitablereagent.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided aprocess for the preparation of a modified kaolin, which comprises arepeated expansion and contraction of kaolin layers using suitablereagent(s). Each cycle of expansion and contraction progressivelymodifies the structure of a starting kaolin by introducing anunspecified type of disorder/order. The repetition of those cycles arecontinued to a level where the resulting kaolin is (significantly)structurally different from the starting kaolin and has significantlygreater capacity to intercalate salts and compounds of non-univalentcations.

Although it is believed that the first cycle of expansion andcontraction causes some structure level changes, its effect is hardlynoticeable in terms of observable fundamental characteristics of thekaolin or significantly increased capacity to intercalate in the casewhere the kaolin has a relatively high degree of disorder. An object ofthe invention is the process of repeated expansion and contraction ofthe layers, and the unexpected discovery that each subsequent cyclecontinues to modify the structure, resulting in significant improvementin intercalation properties of the kaolin after a number of cycles.

Expansion of kaolin layers is effected by intercalation. Any reagentwhich can readily penetrate layers of untreated kaolin would be suitablefor this process. The review by Carr et al., 1978, Clays and ClayMinerals 26 144-152 lists a number of compounds which can intercalateinto untreated kaolins. The preferred reagent is a polar molecule suchas potassium acetate (KAc), dimethylsulfoxide (DMSO), n-methylformamide(NMF) or any other similar species able to expand untreated kaolins. Theuse of any organic or inorganic molecule is suitable in this preferredmethod.

The intercalation can be effected and controlled by many methods knownto those skilled in the art, such as by increasing the temperature orconcentration of the reagents in a mixture with kaolin group minerals.Preferably, the mixture is a dispersed suspension of kaolin and reagentalthough other methods of intercalation for kaolin group minerals areknown. The reagent concentration and solid to solution ratio can bevaried depending on the type of kaolin and type of reagent. Temperatureof the reaction may be controlled anywhere between room temperature and200° C. Obviously, at temperatures higher than 100° C., a suitablereaction vessel to contain the resulting pressure would be required.

Alternatively, the kaolin can be intercalated by grinding the clay witha solid reagent for a suitable length of time as described by Mackinnonet al., 1995, "Grinding of kaolinite improves intercalate yield" In:Clays: Controlling the Environment, Proc. 10th Int. Clay Conf.,Adelaide, Australia, 1993, pp 196-200, G. J. Churchman, R. W.Fitzpatrick and R. A. Eggleton, Editors. Kaolins can also beintercalated by exposure to vapours of volatile compounds at a suitabletemperature and pressure.

The intercalation is then followed by a de-intercalation process so thatthe intercalant is removed from the interlayer and the kaolin layers arecontracted. The de-intercalating process can be effected by washing theintercalate with water if intercalating compounds are soluble in water.In the case of volatile organic compounds, such as DMSO and NMF,de-intercalation can also be effected by mild heating of the intercalatein air. In some cases, de-intercalation can take place by simplydiluting the intercalating solution below a critical concentration.

In a preferred form, the repeated process of intercalation andde-intercalation is effected without washing the slurry, which isconsiderably low-cost as it eliminates the need for repeatedcentrifugation of the clay slurries. According to this process, clay ismixed with a solution of intercalant in water. The concentration ofintercalant is gradually increased, by addition of solid intercalant, toexceed the critical concentration (FIG. 3). Preferably, the intercalantconcentration is raised to a level at which most of the clay expands. Asuitable consistency of the slurry to allow gentle mixing is maintained.After complete intercalation has occurred, the concentration of theintercalant is gradually decreased below the critical concentration byadding water while gently mixing the slurry. The concentration isreduced, preferably, to a concentration where most of the clayde-intercalates (C₀). In order to effect intercalation again after thede-intercalation step, the slurry is simply heated to remove the excesswater and raise the intercalant concentration above the criticalconcentration. In brief, the intercalant concentration is varied betweenC₀ and C₁₀₀ (see FIG. 3) by addition and removal of water by heating.The process fully conserves the intercalant during repeated cycles. Heatand water used in the process can also be easily recycled to a largeextent using common methods.

The process of intercalation and de-intercalation can be suitablymonitored by use of conventional characterisation techniques such asX-ray diffraction. For example, in the case of intercalation with KAc,the basal spacings for kaolinite will expand from 0.71 nm to ˜1.4 nmwith intercalation and, with suitable washing and drying, will return to˜0.71 nm upon de-intercalation. However, as this process approachesformation of modified kaolin the basal spacings remain substantiallyhigher than that of the original kaolinite.

The number of cycles required depends on the nature of the startingkaolin group mineral. However, the number of cycles are usually morethan 10 and can be as high as 60 depending on the type of kaolin, typeof intercalant and temperature of reaction. In a preferred form ofinvention, the process of intercalation and de-intercalation is repeatedmany times, preferably for greater than twenty times, depending on thereagent used, although similar effects can be observed for mostkaolinites with lower levels of intercalation and de-intercalation.

Since the number of cycles required depends on the nature of thestarting kaolin, it is conceivable that natural kaolins can be foundwhich only need 2-10 cycles to achieve the desired properties.

After treating with a desired number of expansion and contractioncycles, the final kaolin product is thoroughly washed to remove theintercalating agent. The product can then be dried or kept wet iffurther intercalation with complex ions is required.

The fundamental characteristics of the modified kaolin depend to a largeextent on the characteristic of the type of starting kaolin, but theyshow a significant modification with respect to the starting kaolin. Forexample, typical XRD pattern of dry modified kaolinite and its startingkaolinite (Georgia kaolinite KGa-1) are given in FIG. 4, and XRD dataderived from XRD patterns are given in TABLE 1. As shown, thesefundamental characteristics indicate that the resulting product isconsistent with kaolin (e.g. a basal spacing of ˜0.71 nm). However, thecritical basal diffraction peaks of the modified kaolinite areconsiderably broader than those of starting kaolinite, indicating largescale exfoliation of the layers and/or widening of the layer spacings.The exfoliated nature kaolin particles is also demonstrated bytransmission electron micrographs of the modified kaolinite (FIG. 5).Similarly, there is considerable change in the relative intensities ofcertain reflections, suggesting atomic scale modification of thestructure. The chemical composition is consistent with the startingkaolinite (TABLE 2).

Furthermore, other properties such as ability to exchange or absorbother chemical species are significantly enhanced compared with theoriginal kaolinite. For example, modified kaolin readily intercalateswith salts of divalent metals such as Ca and Mg, whereas untreatedkaolins do not intercalate with these salts. In FIG. 6 are shown the XRDpattern of modified kaolinite and untreated kaolinite intercalated withCaCl₂ according to the procedure outlined in EXAMPLE 8. As is evident inthese patterns, modified kaolinite has formed a well developedintercalate with CaCl₂, indicated by expansion of the layer spacing,whereas kaolinite shows no intercalation. A similar intercalationaffinity of modified kaolinite towards MgCl₂ is demonstrated in FIG. 7.

Examples of modified kaolinite with increased cation exchange capacity(CEC) values over the original starting kaolin are given in TABLE 3. CECwas determined by exchanging cations with NH₄ ⁺ using the procedureoutlined in International Publication No. WO96/18577. In anotherpreferred form, the resulting powder of modified kaolin can absorb twiceas much water as the starting kaolin. TABLE 4 demonstrates the capacityof modified kaolin to absorb water compared with that for halloysite asnoted in EXAMPLE 5.

The modified form of kaolin is then suitable for further processing ormodification to produce desired intercalates or metal impregnatedkaolins. Alternatively modified kaolin can be further processed to formamorphous derivatives with useful properties such as high cationexchange capacity, high surface area, high oil absorption or all ofthese properties in useful combinations.

An application of this modified kaolin is the formation ofmetal-impregnated or compound impregnated kaolins due to its readinessto intercalate a range of compounds. For example, modified kaolin can bereadily intercalated with alkaline earth metal salts such as MgCl₂,CaCl₂ and transition metal salts such as CuCl₂. In this instance, theuptake of a metal salt is significantly enhanced over that possible bykaolinite (little or no uptake is possible) by the formation of themodified kaolin via an intercalation route. After drying anddehydroxylation as hereinafter described, atomic scale mixtures of theinserted metal with aluminosilicate is produced.

Similarly, new materials with properties suitable for use in ceramics,catalysis or other chemical reactions may be made from the production ofmodified kaolin through the intercalation of such polar inorganicmolecules and subsequent intercalation of other salts.

According to another aspect of the present invention, there is provideda process to prepare microporous materials with high surface area andcation exchange capacity. The modified kaolins prepared by the processdisclosed above are particularly suitable as a starting materials forthis process.

The initial step of this aspect of the invention includes thepreparation of salt impregnated kaolins by intercalation (FIG. 8A).Modified kaolins are particularly suitable as starting materials forthis process due to their capacity to intercalate a variety of salts.Salts may includes halides, nitrates, sulphates of alkali and alkalineearth metals. The halides of alkali earth metals are particularlysuitable for this process.

The second step of this aspect of the invention involves thedehydroxylation of impregnated kaolin preferably by application of heatat a temperature of between 300-900° C. and more preferably 550° andsubsequent washing of the product to remove excess salt and anybyproduct (FIG. 8B). This step is intended to irreversibly dehydroxylatekaolin clay while the inserted metal ions are present within the unitlayers. As a consequence of this step, rows of metal ions are locked inthe network of Si and Al tetrahedra of the metakaolin-like material. Theproduct after this step has a low surface area and cation exchangecapacity, usually comparable with metakaolin.

In the third step of this aspect of the invention, the inserted metalions are preferentially extracted out of the Si-Al oxide framework byreacting with a suitable acid (FIG. 8C). Any inorganic or organic acidin a suitable concentration may be used to extract the inserted metal.Hydrochloric and acetic acid are particularly suitable for this process.All of the inserted metal ions may be extracted or extraction may bestopped to extract only a part of the inserted ions. Depending on thetype and concentration of the acid used some of the Al may also beextracted. The extraction procedure may be modified to achieve thedesired properties of the final product. After partial or completeremoval of the inserted metal ions, the material is left with a porousnetwork of Si and Al tetrahedra, with a surface area 10-30 times greaterthan the starting material. In specific controlled conditions,microporous materials of pore sizes<2 nm are generated with significantmicroporous volume demonstrated by their Type I isotherm (BDDTclassification originally proposed by Brunauer et al., 1940, Journal ofAmerican Chemical Society 62 1723).

Such microporous materials suitably have a BET surface area of between45 and 400 m² g⁻¹ and a CEC of between 50-450 milliequivalents per 100g.

Since the inserted metal is preferentially extracted to a large extent,i.e. without dismantling the framework of Si-Al tetrahedra, theresulting material is left with a significant cation exchange capacity.

The invention also includes within its scope, a modified kaolin notbeing an intercalate having the following properties:

(i) an increased interlayer space compared to corresponding kaolin groupminerals;

(ii) an increased susceptibility to intercalation by cations, anions orsalts compared to corresponding kaolin group minerals; and

(iii) an increased exfoliated morphology compared to correspondingkaolin group minerals.

Such crystalline modified kaolins preferably have an increased fullwidth half maximum (FWHM) for XRD reflections compared to correspondingkaolin group materials.

In regard to the above, the term "corresponding kaolin group minerals"refers to the starting material which is used in the process of theinvention to prepare the modified kaolin of the invention. For example,kaolinite when used as a starting material, will enable a modifiedkaolinite to be prepared by the process of the invention.

After describing the broad conceptual framework of the invention, thefollowing examples are given to further illustrate the preferred aspectsof present invention, and are not intended to limit the scope ofinvention to the specific conditions described therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the structure of 2:1 clayminerals such as montmorillonites and bentonite. The structure of theseclays are composed of a Al-sheet sandwiched between two Si-sheets;

FIG. 2 is a schematic diagram illustrating the 1:1 structure of kaolinclays such as kaolinite, halloysite, dickite and nacrite. The interlayerregion of these minerals is lined by hydroxyls and oxygens;

FIG. 3 is an idealised plot of intercalant concentration versusintercalation intensity;

FIG. 4 show powder XRD patterns;

FIG. 5 is a transmission electron micrograph of modified kaolinite asprepared in EXAMPLE 1. The exfoliation of kaolinite layers can beclearly seen;

FIG. 6 show XRD traces for kaolinite and modified kaolinite aftertreatment with saturated solutions of CaCl₂ ;

FIG. 7 show XRD traces for modified kaolinite washed with saturatedsolution of MgCl₂ and modified kaolinite washed with water to removeintercalated MgCl₂ ;

FIG. 8 is a schematic diagram illustrating the major processing steps inpreparation of the porous materials from modified kaolin clays;

FIG. 9 show XRD traces for basal reflections of original kaolinite,kaolinite intercalated with KAc and modified kaolinite produced afterseveral cycles of intercalation and washing;

FIG. 10 show XRD traces for basal reflections of original dryhalloysite, halloysite intercalated with Kac and modified halloysiteproduced after several cycles of intercalation and washing;

FIG. 11 show XRD traces for modified halloysite and modified halloysitewashed with saturated solution of CaCl₂ ;

FIG. 12 show XRD traces for modified halloysite and modified halloysitewashed with saturated solution of MgCl₂ ;

FIG. 13 is an XRD trace of Ca-loaded alumino silicate material;

FIG. 14 is an XRD trace of Mg-loaded alumino silicate material;

FIG. 15 is a N₂ BET full isotherm of microporous materials preparedfollowing EXAMPLES 12 and 13;

FIG. 16 is an XRD trace of porous material prepared via MgCl₂-intercalation, dehydroxylation and acid extraction as outlined inEXAMPLE 13; and

FIG. 17 is an XRD trace of Cu-loaded alumino silicate material.

EXAMPLES Example 1 Preparation of Modified Kaolin from Kaolinite viaPotassium Acetate Intercalation

Ten grams of kaolinite supplied by Commercial Minerals ("Microwhitekaolin") is thoroughly mixed with 50 ml of saturated solution ofpotassium acetate (KAc) in a beaker. The suspension is allowed tointercalate at room temperature for three days or at a highertemperature up to 80° C. (for lesser times) with progress of theintercalation reaction monitored by conventional X-ray diffraction(XRD). After most of the kaolin has expanded, indicated by change ofbasal spacing from 0.7 nm to 1.4 nm, the suspension is centrifuged andthe saturated solution of KAc is removed/decanted. In order todeintercalate the salt, 50 ml of deionized water is added to the clayand thoroughly mixed. The completion of de-intercalation is confirmed bythe return of basal spacings to the original value of 0.7 nm. Thesuspension is centrifuged again to remove excess water. The clay is thenready for the next cycle of intercalation and de-intercalation which isrepeated several times. An intercalation time of 30 minutes insubsequent cycles (rather than 3 days at room temperature for the firstintercalation) is usually sufficient for maximum intercalation. Again,progress of an intercalation or de-intercalation step is monitored bythe basal spacing of the clay using XRD. Each cycle progressivelymodifies the layer stacking of kaolinite resulting in increasingreadiness for intercalation with each subsequent cycle. In asufficiently modified kaolinite which has been subjected to successivecycles (e.g. >20) of intercalation and de-intercalation, the basalspacing is significantly greater than 0.7 nm due to intercalation ofwater in the modified kaolinite. After the finalintercalation/de-intercalation cycle, the sample is thoroughly washedand dried and subjected to a series of characterisation tests.

FIG. 9 shows the XRD patterns for (i) the original kaolinite; (ii) anexpanded kaolinite with intercalated KAc; and (iii) wet modifiedkaolinite. XRD pattern of dry modified kaolinite along with untreatedkaolinite is shown in FIG. 4. TABLE 2 shows summary data for thismodified kaolinite prepared using KAc.

Example 2 Preparation of Modified Kaolin using Halloysite and PotassiumAcetate Intercalation

Ten grams of halloysite supplied by Commercial Minerals (New Zealandchina clay) is thoroughly mixed with 50 ml of saturated solution of KAcin a beaker. The suspension is allowed to intercalate at roomtemperature for three days or at a higher temperature up to 80° C. (forlesser times) with progress of the intercalation reaction monitored byconventional XRD. After most of the kaolin has expanded, indicated bychange of basal spacing from 0.7 nm to 1.4 nm, the suspension iscentrifuged and the saturated solution of KAc is removed/decanted. Inorder to deintercalate the salt, 50 ml of deionized water is added tothe clay and thoroughly mixed. The completion of de-intercalation isconfirmed by the return of basal spacings to the original value. Thesuspension is centrifuged again to remove excess water. The clay is thenready for next cycle of intercalation and de-intercalation which isrepeated several times.

An intercalation time of 30 minutes in subsequent cycles (rather than 3days at room temperature for the first intercalation) is usuallysufficient for maximum intercalation. Again, progress of anintercalation or de-intercalation step is monitored by the basal spacingof the clay using XRD. Each cycle progressively modifies the layerstacking of kaolinite resulting in increasing readiness forintercalation with each subsequent cycle.

In a sufficiently modified kaolinite which has been subjected tosuccessive cycles (e.g. >20) of intercalation and de-intercalation, thebasal spacing is significantly greater than 0.7 nm due to intercalationof water in the modified kaolinite. After the finalintercalation/de-intercalation cycle, the sample is thoroughly washedand dried and subjected to a series of characterisation tests.

FIG. 10 shows the XRD patterns for (i) the original kaolinite; (ii) anexpanded kaolinite with intercalated Kac; and (iii) the modifiedkaolinite. TABLE 2 shows summary data for this modified halloysiteprepared using KAc as intercalant.

Example 3 Preparation of Modified Kaolin from Kaolinite viaDimethylesulphoxide Intercalation

Ten grams of kaolinite supplied by Commercial Minerals ("Microwhitekaolin") is thoroughly mixed with 50 ml of dimethylesulphoxide (DMSO)containing 8% water. The suspension is allowed to intercalate at roomtemperature for three days or at a higher temperature up to 80° C. (forlesser times) with progress of the intercalation reaction monitored byconventional XRD. After most of the kaolin has expanded, indicated bychange of basal spacing from 0.7 nm to 1.4 nm, the suspension iscentrifuged and the DMSO solution is removed/decanted. In order toeffect de-intercalation, 50 ml of deionized water is added to the clayand thoroughly mixed. The completion of de-intercalation is confirmed bythe return of the basal spacing to the original value of 0.7 nm. Thesuspension is centrifuged again to remove excess water. The clay is thenready for the next cycle of intercalation and de-intercalation which isrepeated many times.

An intercalation time of 30 minutes in subsequent cycles is usuallysufficient for maximum intercalation. Again, progress of anintercalation or de-intercalation step is monitored by the basal spacingof the clay using XRD. Each cycle progressively modifies the layerstacking of kaolinite resulting in increasing readiness forintercalation with each subsequent cycle.

In a sufficiently modified kaolinite which has been subjected tosuccessive cycles (e.g. >20) of intercalation and de-intercalation, thebasal spacing is significantly greater than 0.7 nm due to intercalationof water in the modified kaolinite. After the finalintercalation/de-intercalation cycle, the sample is thoroughly washedand dried and subjected to a series of characterisation tests.

An XRD pattern similar to that shown in FIG. 4 is produced for themodified kaolinite formed by this method. TABLE 2 shows summary data forthis modified kaolinite using DMSO as intercalant.

Example 4 Conversion of Modified Kaolinite to an Amorphous-silicateDerivative

The sample prepared by the final intercalation step outlined in EXAMPLE1 is heated at 550° C. for one hour. The resulting powder shows acharacteristic amorphous trace using XRD and shows an increased CECvalue (using the 1M NH₄ Cl exchange method) over the value for amodified kaolinite as formed in EXAMPLE 1 and a significantly increasedCEC value compared to the starting kaolinite.

TABLE 2 details the surface area and CEC values for this modificationcompared with the starting kaolinite.

Example 5 Absorption of Water by Modified Kaolinite-comparison withKaolins.

Five grams of oven dried modified kaolin and untreated kaolins werewetted with excess deionized water. The resulting slurry was centrifugedat 3000 rpm for 15 minutes to remove superfluous water (i.e. water notretained by the material). The water content of sedimented material wasdetermined gravimetrically and is presented as percent water absorbedfor each sample. In each case, the modified kaolin shows a higher levelof water absorption than original starting kaolin. A similar capacityfor increased absorption of oils and organic molecules can be expectedfor these modified kaolinites.

Example 6 Conversion of Modified Kaolinite to CaCl₂ -intercalated Form

A 5 g sample of kaolinite from Georgia USA (Source Clay KGa-1) isconverted to a modified kaolin via intercalation of KAc as demonstratedin EXAMPLE 1. After formation of the KAc-kaolinite intercalate, it iswashed with saturated CaCl₂ solution and characterised using powder XRD.

An example of powder XRD traces for the sample after washing with CaCl₂and after washing again with water (to remove CaCl₂) is given in FIG. 6.

Example 7 Conversion of Modified Kaolinite to MgCl₂ -intercalated Form

A 5 g sample of kaolinite from Georgia USA (Source Clay KGa-1) isconverted to a modified kaolin via intercalation of KAc as demonstratedin EXAMPLE 1. After formation of the KAc-kaolinite intercalate, it iswashed with saturated MgCl₂ solution and characterised using powder XRD.

An example of powder XRD traces for the sample after washing with MgCl₂and after washing again with water (to remove MgCl₂) is given in FIG. 7.

Example 8 Conversion of Halloysite to Modified Halloysite and SubsequentIntercalation of CaCl₂

A 10 g sample of New Zealand china clay (halloysite HNZ) is converted toa modified kaolin via intercalation of KAc as demonstrated in EXAMPLE 2.The modified halloysite, kept wet after its preparation, is then washedtwice with a saturated solution of CaCl₂. The modified halloysitereadily intercalates CaCl₂ as demonstrated by the expansion of the layerto 1.4 nm (FIG. 11).

Example 9 Conversion of Halloysite to Modified Halloysite and SubsequentIntercalation of MgCl₂

A 10 g sample of New Zealand china clay (halloysite HNZ) is converted toa modified kaolin via intercalation of KAc as demonstrated in EXAMPLE 2.The modified halloysite, kept wet after its preparation, is then washedtwice with a saturated solution of MgCl₂. The modified halloysitereadily intercalates MgCl₂ as demonstrated by the expansion of the layerto 1.4 nm (FIG. 12).

Example 10 Preparation of Ca Loaded Alumino Silicate Material

A 5 g sample of modified halloysite prepared as in EXAMPLE 2 isintercalated with a saturated solution of CaCl₂ as described in EXAMPLE8. The kaolin- CaCl₂ intercalate so prepared is then dried at 80° C.before it is heated at 550° C. for one hour. The sample is then allowedto cool before washing the powder until all soluble salt is removed. Theresulting white powder retains the inserted Ca in the structure of thedehydroxylated material.

The chemical composition of this material is given in TABLE 4 and an XRDtrace is given in FIG. 13.

Example 11 Preparadon of Mg Loaded Alumino Silicate Material

A 5 g sample of modified halloysite prepared as in EXAMPLE 2 is interdescribed in EXAMPLE 9. The kaolin- MgCl₂ intercalate so prepared isthen dried at 80° C. before it is heated at 550° C. for one hour. Thesample is then allowed to cool before washing the powder until allsoluble salt is removed. The resulting white powder retains the insertedMg in the structure of the dehydroxylated material.

The chemical composition of this material is given in TABLE 4 and an XRDtrace is given in FIG. 14.

Example 12 Preparation of Porous Material using ModifiedKaolin-CaCl2-intercalate

A 10 g sample of halloysite is converted to modified halloysite and thenintercalated with CaCl₂ according to the procedure outline in EXAMPLE 8.The intercalated material is then dehydroxylated and washed as inEXAMPLE 10. This material is then mixed with 40 ml of 0.5 M HCl. Thecontents were then allowed to react for two hours while being stirred atroom temperature. Next, the contents are centrifuged and supernatantdiscarded. The solid material is washed several times with deionizedwater and then dried at 105° C. The final product has a surface area of110 m² /g and CEC of 52 meq/100 g. The material has a significantmicroporosity as demonstrated by N₂ BET isotherm which is of Type 1(FIG. 15). An unmodified halloysite given the same acid activationtreatment has a surface area and CEC values of 24 m² /g and 5 meq/100 g,respectively.

Example 13 Preparadon of Porous Material using the Modified Kaolin-MgCl₂Intercalate and HCl

A 10 g sample of halloysite is converted to modified halloysite and thenintercalated with MgCl₂ according to the procedure outline in EXAMPLE 9.The intercalated material is then dehydroxylated and washed as inEXAMPLE 11. This material is then mixed with 40 ml of 0.5 M HCl. Thecontents are then allowed to react for two hours while being stirred atroom temperature. Next, the contents are centrifuged and supernatantdiscarded. The solid material is washed several times with deionizedwater and then dried at 105° C. The final product has a surface area of205 m² /g and CEC of 67 meq/100 g. The materials has a significantmicroporosity as demonstrated by N₂ BET isotherm which is of Type 1(FIG. 15) and XRD trace FIG. 16 showing a broad diffraction peak at ˜15Å.

An unmodified halloysite given the same treatment has a surface area andCEC values of 24m² /g and 5 meq/100 g, respectively.

Example 14 Preparation of Porous Material using the ModifiedKaolin-MgCl₂ Complex and Acetic Acid

A 10 g sample of halloysite is converted to modified halloysite and thenintercalated with MgCl₂ according to the procedure outlined in EXAMPLE9. The intercalated material is then dehydroxylated and washed as inEXAMPLE 11. This material is then mixed with 40 ml of 1 M acetic acid.The contents are then allowed to react for two hours while being stirredat room temperature. Next, the contents are centrifuged and supernatantdiscarded. The solid material is washed several times with deionizedwater and then dried at 105° C. The final product has a surface area of267 m² /g. The materials showed a N₂ BET isotherm which is of Type 1 andXRD trace similar to that shown in FIG. 16.

Example 15 Preparation of Cu-load Alumino Silicate

A 10 g sample of halloysite is converted to modified halloysiteaccording to procedure outlined in EXAMPLE 2. The modified kaolin isthen intercalated with saturated solution CuCl₂ at 100° C. for 3 days.After intercalation, the free CuCl₂ solution is removed. Theintercalated material is dried and then heated at 550° C. for 1 hour.The product is then washed and analysed for Cu content, surface area andcrystallinity. The final product contains 25.9% CuO and shows an XRDpattern as presented in FIG. 17. A similarly processed unmodifiedhalloysite retained no or little Cu.

TABLES

                  TABLE 1                                                         ______________________________________                                        Crystallographic data for untreated and modified kaolinite                    prepared as in EXAMPLE 1.                                                     UNTREATED KAOLINITE MODIFIED KAOLINITE                                        hki   d (Å)                                                                             FWHM      l/l   d (Å)                                                                           FWHM   l/l                                ______________________________________                                        001   7.11    0.219     100   7.17  0.57   100                                020   4.44    2.25      31    4.44  --     25                                 110   4.34    --        37    4.34  --     24                                 111   4.16    0.35      28    4.16  --     19                                 021   3.83    --        13     3.852                                                                              --     10                                 002   3.56    0.24      76    3.56  0.35   91                                 111   3.36    --         7    3.36  --      7                                 130   2.56    0.361     20    2.56  0.432  17                                 131   2.52    --        15    2.52  --     12                                 132   2.49    0.337     23    2.49  0.418  16                                 003   2.38    --         9    2.37  --     10                                 131   2.33    0.406     32    2.34  0.55   25                                 131   2.29    --        19    2.29         14                                 203   1.99    0.54       8    1.99  0.676   8                                 133   1.66    --        12    1.66         11                                 331   1.49    0.39      19    1.49  0.467  15                                 ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Averaged microprobe analyses for untreated kaolinite and                      modified kaolinite prepared as outlined in EXAMPLE 1.                         ELEMENT WT %    MODIFIED  UNTREATED                                           OXIDE           KAOLINITE KAOLINITE                                           ______________________________________                                        Na.sub.2 O      0.01      .01                                                 N.sub.2 O       1.2       .01                                                 Al.sub.2 O.sub.3                                                                              35.8      35.2                                                SiO.sub.2       50.0      49.7                                                Fe.sub.2 O.sub.3                                                                              0.8       0.9                                                 TOTAL           87.8      85.8                                                ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Summary of properties for selected modifications of                           kaolinite                                                                                    SURFACE AREA CEC                                               SAMPLE         (m.sup.2 /g) (meq/100 g)                                       ______________________________________                                        Untreated kaolins                                                             KCM kaolinite (untreated)                                                                    24           37                                                KGa-1 kaolinite (untreated)                                                                  10           25                                                HNZ halloysite (untreated)                                                                   21           33                                                Modified kaolins                                                              KCM Example 1  23           87                                                HNZ Example 2  21           73                                                KGa-Example 3  12           91                                                KCM Example 4  18           242                                               Comparative Data                                                              Metakaolin     10           28                                                Calcined kaolin                                                                              21            5                                                ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Relative absorption of water for modified kaolins                             SAMPLE          WATER ABSORPTION (%)                                          ______________________________________                                        KCM kaolinite (untreated)                                                                     106                                                           HNZ halloysite (untreated)                                                                     58                                                           Modified kaolins                                                              KCM Example 1   212                                                           HNZ Example 1   205                                                           ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Averaged microprobe analyses for metal impreganted                            modified kaolins                                                              ELEMENT WT % OXIDE                                                                          Ca-INTERCALATE                                                                             Mg-INTERCALATE                                     ______________________________________                                        CaO           10.60        --                                                 MgO           --           20.08                                              Na.sub.2 O    --           --                                                 K.sub.2 O     2.44         3.19                                               Al.sub.2 O.sub.3                                                                            34.17        27.87                                              SiO.sub.2     47.97        39.71                                              Fe.sub.2 O.sub.3                                                                            0.30         0.26                                               TOTAL         95.48        91.11                                              ______________________________________                                    

Legends

FIG. 3

C₀ represent the concentration at which all clay is deintercalated andC₁₀₀ represents the intercalant concentration at which all clay isintercalated.

FIG. 4

Powder XRD patterns for (a) standard kaolinite (KGa-1) and (b) drymodified kaolinite prepared as outlined in Example 1. The modifiedkaolinite shows well resolved basal and hk reflections. The (00)reflections of modified kaolinite, marked by asterisk and (001) enlargedin (d) are significantly broader than corresponding reflections ofuntreated kaolinite (c).

FIG. 6

XRD traces for (a) kaolinite and (b) modified kaolinite after treatingwith saturated solution of CaCl₂. Modified kaolinite expands to formCaCl₂ intercalate, indicated by appearance of a refection at 8.7° twotheta angle (˜10 Å), and reduction in intensity of 12.4° reflectionwhereas layer spacings of kaolinite remains unchanged at 7 Å indicatedby strong reflection at 12.4° two theta angle.

FIG. 7

XRD traces for (a) modified kaolinite washed with saturated solution ofMgCl₂ and (b) modified kaolinite washed with water to removeintercalated MgCl₂. Modified kaolinite has intercalated MgCl₂intercalate, indicated by appearance of a refection at 8.7° two thetaangle (˜10 Å), whereas raw kaolinite similarly treated showed XRD tracesimilar to FIG. 6A.

FIG. 9

XRD traces for basal reflections of (a) original kaolinite, (b)kaolinite intercalated with KAc and (c) modified kaolinite producedafter several cycles of intercalation and washing. Original kaolinitehas a layer spacing of 7 Å, expands to about 14 Å after intercalationwith KAc and returns to 7 Å after washing the KAc. After several cyclesof expansion and contraction, kaolinite spacing does not return to 7 Å.A residual peak at 7 Å represents kaolinite which is not affected bythis treatment.

FIG. 10

XRD traces for basal reflections of (a) original dry halloysite, (b)halloysite intercalated with KAc and (c) modified halloysite producedafter several cycles of intercalation and washing.

FIG. 11

XRD traces for (a) modified halloysite and (b) modified halloysitewashed with saturated solution of CaCl₂ Intercalation of modifiedhalloysite with CaCl₂ is indicated by expansion of layers.

FIG. 12

XRD traces for (a) modified halloysite and (b) modified halloysitewashed with saturated solution of MgCl₂ Intercalation of modifiedhalloysite with MgCl₂ is indicated by expansion of layers from 10 Å to15.5 Å.

FIG. 13

XRD traces of Ca impregnated kaolin composition. The material is largelyamorphous. The sharp reflections belong to quartz which occur asimpurity in the starting material.

FIG. 14

The material is largely amorphous. The sharp reflections belong toquartz which occur as impurity in the starting material.

FIG. 15

The isotherms are classified as Type 1 indicating significantmicroporosity.

FIG. 16

A broad reflection at about 6° two theta angle demonstrates the presenceof micropores.

We claim:
 1. A process for the preparation of a modified kaolin from akaolin group mineral comprising repeatedly expanding and contracting thelayers of the kaolin group mineral, said layers comprising oneSi-tetrahedral sheet and one Al-octahedral sheet to form a modifiedkaolin, which is not an intercalate, said modified kaolin also having agreater intercalation capacity than a kaolin which has not undergonerepeated expansion and contraction.
 2. A process as claimed in claim 1wherein said repeated expansion and contraction of the layers comprises10-60 cycles.
 3. A process as claimed in claim 1 wherein the repeatedexpansion and contraction of the layers comprises 2-10 cycles.
 4. Aprocess as claimed in claim 1 wherein the repeated expansion andcontraction of the layers comprises 20-60 cycles.
 5. A process asclaimed in claim 1 wherein said repeated expansion and contraction isinitiated by initial intercalation of a reagent which can penetratekaolin layers to reach an interlayer region therebetween to form anintercalate.
 6. A process as claimed in claim 5 wherein the reagent is apolar molecule.
 7. A process as claimed in claim 6 wherein the polarmolecule is selected from potassium acetate, dimethyl sulfoxide orN-methyl formamide.
 8. A process as claimed in claim 5 wherein theintercalation is effected by grinding the kaolin group mineral with asolid reagent.
 9. A process as claimed in claim 5 wherein theintercalation is carried out by exposing the kaolin group mineral tovapors of volatile compounds.
 10. A process as claimed in claim 5wherein the intercalation is followed by deintercalation which involvesremoval of the reagent.
 11. A process as claimed in claim 10 wherein thedeintercalation is effected by washing the intercalate with water in thecase where the reagent is soluble in water.
 12. A process as claimed inclaim 10 wherein the reagent is removed by heating of the intercalate inair.
 13. A process as claimed in claim 10 wherein the reagent is removedby dilution of the reagent to a concentration lower than a concentrationwhere most of the kaolin deintercalates (C₀).
 14. A process as claimedin claim 10 wherein the procedure of intercalation and deintercalationis repeated without washing of the intercalate.
 15. A process as claimedin claim 14 wherein the kaolin group mineral is mixed with a solution ofreagent in water and the concentration of reagent is gradually increasedby addition of solid reagent until the reagent's concentration exceeds aconcentration at which the kaolin is fully intercalated (C₁₀₀).
 16. Aprocess as claimed in claim 15 wherein the reagent concentration ismixed to a level at which most of the kaolin group mineral expands. 17.A process as claimed in claim 15 wherein after complete intercalationhas occurred, the concentration of the reagent is gradually decreasedbelow the C₁₀₀ concentration by adding water to the mixture with mildagitation.
 18. A process as claimed in claim 17 wherein theconcentration of the reagent is reduced to a concentration where most ofthe kaolin deintercalates.
 19. A process as claimed in claim 18 whereinintercalation again takes place by heating of the mixture to removeexcess water and raise the concentration of reagent above the C₁₀₀concentration.
 20. A process as claimed in claim 19 wherein the reagentconcentration is varied between a concentration where most of the kaolindeintercalates (C₀) to a concentration above the C₁₀₀ concentration byaddition and removal of the reagent by heating.
 21. A process as claimedin claim 5 wherein the modified kaolin is subjected to intercalationwith a metal salt to form said intercalate.
 22. A process as claimed inclaim 21 wherein the metal salt is a salt of a divalent cation.
 23. Aprocess as claimed in claim 22 wherein the metal salt is a magnesium,calcium or copper salt.
 24. A process as claimed in claim 21 wherein theintercalate is subsequently heated to between 300-900° C. todehydroxylate the intercalate.
 25. A process as claimed in claim 24wherein the temperature is 550° C.
 26. A process as claimed in claim 24wherein the intercalate after heating is washed to remove excess reagentand any other byproduct or contaminant.
 27. A process as claimed inclaim 26 wherein inserted metal ions are extracted from the intercalateby reaction with an acid to form a microporous material.
 28. A processas claimed in claim 27 wherein the acid is hydrochloric acid or aceticacid.
 29. A modified kaolin when prepared by the process of any one ofclaims 1-20.
 30. An intercalate formed by the process of claim
 21. 31.An intercalate as claimed in claim 30 wherein the salt is a divalentsalt inclusive of salts of magnesium, calcium and copper.
 32. Adehydroxylated kaolin formed by the process of claim
 26. 33. Crystallinemodified kaolins not being intercalates having the followingproperties:(i) an increased interlayer space compared to unmodifiedkaolins which have not undergone repeated expansion and contraction;(ii) an increased susceptibility to intercalation by cations, anions orsalts compared to unmodified kaolins which have not undergone repeatedexpansion and contraction; (iii) an increased exfoliated morphologycompared to unmodified kaolins which have not undergone repeatedexpansion and contraction: and (iv) an increased intercalation capacitycompared to unmodified kaolins which have not undergone repeatedexpansion and contraction.
 34. Crystalline modified kaolins as claimedin claim 33 which also have increased Full Half Maximum (FWHM) for X-rayreflections compared to unmodified kaolins.